In conventional systems, the bits of an initialization vector for encrypted content are set to all 0s or some other constant number and do not change while playing back or streaming the media. Repeating the initialization vector while using the same key can allow attackers to infer relationships between segments of the encrypted data and possibly decrypt the data. Randomizing or pseudo-randomizing the initialization vector enables the encryption scheme to be semantically secure, making it difficult for the data to be illegitimately decrypted using only the cipher text.
In stream ciphers, the initialization vectors can be loaded into the key, after which a number of cipher rounds are executed prior to releasing the first bit of output. Reducing the number of rounds using the same initialization vector can increase security as entropy loss and initialization vector related attacks are a potential security issue for stream ciphers. Changing the initialization vector frequently therefore also can increase security.
Changing the initialization vector requires that the initialization vector change is signaled so that the media can be decrypted using the new initialization vector. Signaling and changing the initialization vector can add complexity to the media stack, which can interfere with smooth streaming and playback of media.